The invention relates generally to fullerenes and more particularly to the selective addition of functional compounds and groups to fullerene molecules.
Fullerenes are a family of closed-shell carbon molecules with C.sub.60 as the prototypical member. A C.sub.60 molecule is depicted in FIG. 1. A technique for preparing and isolating macroscopic quantities of fullerenes was reported by Kratschmer et al., Nature 347 (354) (1990), the contents of which are incorporated herein by reference. Since that time, research on fullerenes has been of considerable importance for both its academic and commercial implications.
Research on fullerenes can generally be categorized into two different types. The first relates to the physical and material properties. For example, it has been discovered that when doped with a number of alkali metals, C.sub.60 exhibits high temperature superconductivity, as reported by Haddon, et al., Nature 350 (320) (1990) and Hebard, et al., Nature 350 (600) (1990), the contents of which are incorporated herein by reference.
Other discovered properties of C.sub.60 include (a) organic ferromagnetism when an organic reducing agent is added to C.sub.60 as reported by Allemand, et al., Science 253 (301) (1991); (b) high resilience and stability as reported by Vasallo, et al., J. Am. Chem. Soc. 113(7820) (1991); (c) conversion to diamond by application of asymmetric pressure at room temperature as reported by Reguerito, et al., Nature 355 (237) (1002); (d) nonlinear optical properties as reported by Wang, et al., Appl Phys. Lett. 60 (810) (1992) and Gong, et al., Appl. Phys. 71 (3025) (1992); (e) optical limiting properties as reported by Tutt, Nature 356 (225) (1992); and (f) the trapping and separation of gases as reported by Business Week, p. 101, May 11, 1992. The contents of each of these references is incorporated herein by reference.
The second type of research relates to the chemistry of the fullerene molecules. Chemically, C.sub.60 behaves similarly to electron deficient alkenes and is a mild oxidizing agent. The relatively high electronegativity of fullerenes is thought to be due to the pyracyclic character of certain inter-five-membered ring bonds. Chemical reactions of fullerenes that have been studied, include methylation, as reported by Bausch, et al., J. Am. Chem. Soc. 113 (3205) (1991); hydrogenation as reported by Haufler, et al., J. Phys. Chem. 94 (8634) (1990); fluoration as reported by Selig, et al., J. Am. Chem. Soc. 113 (5475) (1991); epoxidation as reported by Creegan, et al., J. Am. Chem. Soc. 114 (1103) (1992); halogenation as reported by Olah, et al., J. Am. Chem. Soc. 113 (9385) (1991) and Tebbe, et al. J. Am. Chem. Soc. 114 (3977) (1992); and nucleophilic addition as reported by Wudl, et al. Fullerenes: Synthesis, Properties, and Chemistry of Large Carbon Clusters , Hammond, et al. ACS Symp. Series 481, Washington, D.C. 1992, p. 161. The contents of each of these references is incorporated herein by reference.
Although the reactions discussed above have proved to be reproducible at the laboratory level, they have yet to show satisfactory commercial significance. These reactions were all carried out in homogeneous media. A common obstacle for these chemical reactions is the inability to achieve selective functionalization. The inability to control the production of byproducts continues to be the focus of considerable activity.
For example, the chlorination and bromination of C.sub.60 yields a complex mixture of chlorinated products with up to 24 halogen atoms added to the C.sub.60. The nucleophilic addition of amines to C.sub.60 leads to multiple addition products. The copolymerization of C.sub.60 and p-xylylene yields highly crosslinked polymers due to the multiple benzylation of C.sub.60. A more detailed discussion of these reactions can be found in Olah, et al. J. Am. Chem. Soc. 113 (9385) (1991), Wudl. et al. Fullerenes: Synthesis, Properties, and Chemistry of Large Carbon Clusters, Hammond, et al. ACS Symp. Series 481, Washington, D.C. 1992, p. 161, and Loy, et al. J. Am. Chem. Soc. 114 (3977) (1992), the contents of which are incorporated herein by reference.
As is evident from the above, the inability to control these reactions, which produce a mixture which is very difficult to separate and characterize, diminishes the commercial value of these reactions and limits the commercial application of fullerene chemistry. Accordingly, a selective functionalization method is needed in order to fully develop the potentially rich chemistry of fullerenes in a more satisfactory manner.